1. Field of the Invention
The present invention relates to a shaft coupling mechanism, and more particularly to a shaft coupling mechanism for a sewing machine.
2. Description of the Prior Art
Typical sewing machines comprise a rotatable shaft that is required to be coupled to a rotatable spindle for rotating the spindle in an oscillating action without affecting the rotational movement of the shaft. One typical shaft coupling mechanism is shown in FIGS. 5 and 6 and comprises an eccentric 11 secured to a rotatable shaft 10 and rotated in concert with the shaft 10. The eccentric 11 is rotatably engaged in a ring 71 such that the rotational movement of the shaft 10 and the eccentric 11 may cause the ring 71 to move up and down. A bolt 72 has an upper end engaged with the ring 71 and a nut 73 is engaged with the bolt 72 so as to secure the bolt 72 to the ring 71. A coupler 74 is secured to the bottom of the bolt 72 and includes a ball 75 rotatably engaged in a spherical cavity 740 thereof so as to form a ball joint. The ball 75 includes an aperture 750 formed therein for engaging with a bolt 76. Another ring 70 is secured to a spindle 20 and includes an extension 77 secured to the bolt 76 such that the upward and downward movement of the ring 71 and the coupler 74 may cause the spindle 20 to rotate in an oscillating action. However, as shown in FIG. 6, the extension 77 may be engaged with the coupler 74 when the extension 77 and the spindle 20 is rotated for more than 15 degrees such that an external force may be applied onto the coupler 74 and such that the eccentric 11 may have the tendency to be forced to be disengaged from the ring 71. It is to be noted that the ring 70 may be disengaged from the spindle 20 such that the ring 70 may not effectively drive the spindle 20 to rotate. In addition, an expert or a high technique is required for manufacturing the ball joint. It will be difficult to engage the ball 75 within the coupler 74. Furthermore, the manufacturing cost of the ball coupler is very expensive.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional shaft coupling mechanisms.